Experts caution that the findings aren't definitive and may have nothing to do with how the drug works in children and adults with ADHD. Still, the research could lead to better understanding of both Ritalin and the disorder, said co-author Barry Waterhouse, a professor of neurobiology and anatomy at Drexel University, in Philadelphia.

"It will begin to help us understand how ADHD may work," he said.People with ADHD often have trouble focusing on tasks, and may be hyperactive and impulsive. However, some skeptics question whether more people are being diagnosed with ADHD than actually have it.

What's also been unclear is just how Ritalin (methylphenidate) and other stimulants successfully treat as many as 80 percent of ADHD patients -- a success rate higher than any other class of psychiatric drugs, said Dr. David W. Goodman, an assistant professor at Johns Hopkins University and director of the Adult Attention Deficit Disorder Center of Maryland.

In fact, it's "counterintuitive" that Ritalin -- a stimulant -- would dampen ADHD symptoms, noted study co-author Waterhouse. That's because the disorder itself manifests as a form of neurological overstimulation.

Researchers suspect that Ritalin somehow affects neurotransmitters, the chemicals that help signals travel through the brain.

In the new research, Waterhouse and colleagues studied the brains of rats who were given Ritalin and then had their whiskers stroked, to stimulate their brains. Their findings appear in the May 30 online edition of the Journal of Neurophysiology.

Ritalin appeared to change the way the rodents' brains reacted to the stimulus by dampening signals that alert rats that something is going on, Waterhouse said. "The signal is being suppressed, and therefore irrelevant signals are not receiving the same level of brain response" as more important signals, he said.

In essence, the drug may allow the rats to not be easily distracted, he said. According to him, this could reflect what happens in mentally healthy humans who take Ritalin: they become better able to concentrate.

However, the rats in the study weren't an ideal match for human patients, because they didn't have a rodent equivalent of ADHD, Goodman said. While some animals have conditions that reflect human mental illnesses, such as depression or anxiety, he said he's not aware of any animal that develops something like ADHD.

So, while the new study is "interesting," Goodman said, "it's a quantum leap to take the findings and say anything about ADHD in humans."